i$8 THE PRESERVATION OF MILK 



stopper (impervious to bacteria), which is removed only just before use. This is the 

 fundamental idea of the so-called Soxhlet method of sterilising milk, in which 

 several bottles are inserted in a movable frame and immersed in a tin pan con- 

 taining water, which is thereupon kept on the boil for forty minutes. SOXHLET (I.) 

 employs latterly, as automatic stopper, an indiarubber disc resting on the ground 

 mouth of the bottle, and prevented, by means of a loose-fitting tube, from 

 becoming displaced laterally. The gases and steam given off from the milk in 

 boiling escape into the air by forcing up the disc, and when the operation is 

 finished and the apparatus is removed from the fire, this clack-valve is kept 

 tight by the pressure of the outside air, the partial vacuum within the bottles 

 being generally equivalent to 100 mm. of mercury. This stopper not only pre- 

 vents access of air, but also debars dealers or purchasers from opening the bottle 

 with fraudulent intent, since it cannot be closed again. This ensures the pur- 

 chasing public receiving the milk in the same unadulterated condition in which 

 it left the dairy. Similar to Soxhlet's method are those of Egli and Escherich, a 

 short description of which (as also of those of Soltmann, Bertling, Gerber, and 

 Stadtler) will be found in a comparative treatise by EMMA STRUB (I.). 



125. Germ-Content of Milk Treated by the Soxhlet Method. 



The foregoing method would meet all requirements were the destruction of 

 the pathogenic and the lactic acid bacteria alone in question. However, as has 

 previously been mentioned, milk also contains very hardy bacterial spores, able 

 to withstand such a course of boiling as that specified . The number of such 

 spores varies, and is greater in proportion as .the degree of uncleanliness in the 

 attendance on the cows and in the operation of milking increases. These milk 

 bacteria (which resist the ordinary means of sterilisation) were investigated 

 with regard to their properties and action by C. FLTJGGE (II.)- A few of them 

 are very widely diffused, but they do not develop below 18 C. Milk sterilised by 

 mere boiling may therefore be rich in such bacteria and yet keep unaltered for a 

 long time at room temperature, though, if introduced into the alimentary canal 

 of the young infant, the hardy spores develop into rapidly-multiplying bacilli 

 which decompose the constituents of the milk. In such case, not only are 

 copious amounts of gas, giving rise to considerable flatulency, formed, but also 

 poisonous decomposition products of albuminoid matter, which when fed to 

 puppies produce diarrhoea attended with fatal results. 



The danger incurred from this cause is much greater for the nursing infant 

 than for the adult, not only because the latter organism is stronger, but also for 

 the further reason that the dietary of adults is a mixed one, in consequence 

 whereof numerous other bacteria, inimical to those in question, are introduced 

 into the alimentary canal. On the other hand, the result of using such imper- 

 fectly and partially sterilised milk is that the digestive organs of the infant, 

 nourished on milk alone, are converted into a veritable breeding-ground for 

 these poisonous microbes. 



These bacteria are closely allied to the Bacillus mesentericus vidgatus. Fliigge 

 himself described a number of such species; and S. STERLING (I.) added five 

 new ones to the series, naming them with reference to their chemical activity 

 as Bacillus lactis peptonans a, |3, y, 8, e. Attention was drawn at an earlier date, 

 by LOEFFLER (III.) and Emma Strub, to the frequent occurrence of B. mesen- 

 tiricus vu'gatus in milk. 



Attempts have not been lacking on the part of dairy technicistsand bacterio- 

 logists to arrive at a method for annihilating these pests as well. A critical 

 examination of these methods cannot, however, be made here, but any reader 

 desiring fuller details is referred to a comprehensive exposition of the question 



